Soma is several times described as dwelling or growing on the mountains, in accordance with the statements of the Avesta about Haoma. Its true origin and abode is regarded as heaven, whence it has been brought down to earth. This belief is most frequently embodied in the myth of the soma-bringing eagle (çyena), which is probably only the mythological account of the simple phenomenon of the descent of lightning and the simultaneous fall of rain.
In some of the latest hymns of the Rigveda Soma begins to be somewhat obscurely identified with the moon. In the Atharva-veda Soma several times means the moon, and in the Yajurveda Soma is spoken of as having the lunar mansions for his wives. The identification is a commonplace in the Brāhmaṇas, which explain the waning of the moon as due to the gods and fathers eating up the ambrosia of which it consists. In one of the Upanishads, moreover, the statement occurs that the moon is King Soma, the food of the gods, and is drunk up by them. Finally, in post-Vedic literature Soma is a regular name of the moon, which is regarded as being consumed by the gods, and consequently waning till it is filled up again by the sun. This somewhat remarkable coalescence of Soma with the moon doubtless sprang from the hyperbolical terms in which the poets of the Rigveda dwell on Soma’s celestial nature and brilliance, which they describe as dispelling darkness. They sometimes speak of it as swelling in the waters, and often refer to the sap as a “drop” (indu). Comparisons with the moon would thus easily suggest themselves. In one passage of the Rigveda, for instance, Soma in the bowls is said to appear like the moon in the waters. The mystical speculations with which the Soma poetry teems would soon complete the symbolism.
A comparison of the Avesta with the Rigveda shows clearly that soma was already an important feature in the mythology and cult of the Indo-Iranian age. In both it is described as growing on the mountains, whence it is brought by birds; in both it is king of plants; in both a medicine bestowing long life and removing death. In both the sap was pressed and mixed with milk; in both its mythical home is heaven, whence it comes down to earth; in both the draught has become a mighty god; in both the celestial Soma is distinguished from the terrestrial, the god from the beverage. The similarity goes so far that Soma and Haoma have even some individual epithets in common.
The evolution of thought in the Rigvedic period shows a tendency to advance from the concrete to the abstract. One result of this tendency is the creation of abstract deities, which, however, are still rare, occurring for the most part in the last book only. A few of them are deifications of abstract nouns, such as Çraddhā “Faith,” invoked in one short hymn, and Manyu, “Wrath,” in two. These abstractions grow more numerous in the later Vedas. Thus Kāma, “Desire,” first appears in the Atharva-veda, where the arrows with which he pierces hearts are already referred to; he is the forerunner of the flower-arrowed god of love, familiar in classical literature. More numerous is the class of abstractions comprising deities whose names denote an agent, such as Dhātṛi, “Creator,” or an attribute, such as Prajāpati, “Lord of Creatures.” These do not appear to be direct abstractions, but seem to be derived from epithets designating a particular aspect of activity or character, which at first applying to one or more of the older deities, finally acquired an independent value. Thus Prajāpati, originally an epithet of such gods as Savitṛi and Soma, occurs in a late verse of the last book as a distinct deity possessing the attribute of a creator. This god is in the Atharva-veda and the Vājasaneyi-Saṃhitā often, and in the Brāhmaṇas regularly, recognised as the chief deity, the father of the gods. In the Sūtras, Prajāpati is identified with Brahmā, his successor in the post-Vedic age.
A hymn of the tenth book furnishes an interesting illustration of the curious way in which such abstractions sometimes come into being. Here is one of the stanzas:—
By whom the mighty sky, the earth so steadfast,
The realm of light, heaven’s vault, has been established,
Who in the air the boundless space traverses:
What god should we with sacrifices worship?
The fourth line here is the refrain of nine successive stanzas, in which the creator is referred to as unknown, with the interrogative pronoun ka, “what?” This ka in the later Vedic literature came to be employed not only as an epithet of the creator Prajāpati, but even as an independent name of the supreme god.